1. Field of the Invention
The present invention relates to an electron beam apparatus which irradiates a semiconductor substrate (hereinafter referred to as a wafer) or the like with finely focused electron beams. More particularly, the present invention relates to an electron beam apparatus which draws extremely-fine graphic patterns on the wafer, to an electron beam apparatus which inspects patterns drawn on the wafer by observing secondary electrons emitted from the wafer irradiated with electron beams, and to an electron beam apparatus having both drawing and inspecting functions using electron beams.
To be more specific, the present invention relates to an electron beam apparatus which subjects a graphic pattern to be drawn to inverse filtering to sharpen the graphic pattern for the purposes of enhancing the contrast of an exposed image and also speeding up drawing, and to a method of generating an electron beam irradiation pattern.
Moreover, the present invention relates to an electron beam apparatus which irradiates electron beams on a periphery of edges of a pattern to be inspected on a wafer, thereby preventing occurrence of electrostatic charges and improving inspection accuracy.
Furthermore, the present invention relates to an electron beam apparatus which realizes high-speed graphic pattern drawing and wafer inspection by irradiating a wafer with a plurality of electron beams.
2. Description of the Related Art
An electron beam apparatus which draws a graphic pattern on a wafer by use of electron beams is designed to form a desired drawing pattern on a wafer by irradiating electron beams of a given shape onto a wafer coated with a photosensitive material (hereinafter referred to as a resist) which is photosensitive to electron beams, and then by removing the resist, which has been changed in quality due to exposure, by use of chemicals. Conventional electron beam apparatuses include a variable-shaped beam writer, as disclosed in Japanese Patent Application Publication No. Hei 11 (1999)-40485, which passes electron beams through several apertures to form the electron beams of a given shape, and which then exposes a given pattern onto a resist on a wafer. The variable-shaped beam writer is now in wide use. Moreover, in Japanese Patent Application Publication No. Hei 11 (1999)-195589 and Japanese Patent Application Publication No. 2000-508839, a raster scan type electron beam apparatus is disclosed, which uses finely focused spot electron beams to form and expose a pattern of a given shape on a wafer. The raster scan type electron beam apparatus will probably come into wider use in the future as a process will become finer.
It is known that, in the electron beam apparatuses described above, an error arises in a pattern to be exposed, due to a phenomenon called a proximity effect of electron beams even if electron beam is irradiated thereon by using the desired drawing pattern to be drawn. The finer patterns to be exposed are, the greater errors relatively become. Thus causing a significant problem. The proximity effect is a phenomenon in which electron beams, which have reached a wafer, not only expose a resist but also pass through the resist, then scatter inside the wafer, and thus expose the resist again. Although the absolute amount of the electrons is small, the range of scattering reaches a few tens of micrometers (μm). When electron beams are irradiated over a wide range, the amount of exposure reaches a few tens of percent (%) of the threshold of exposure that is the exposure level of the resist. Thus, the proximity effect causes overexposure also outside a portion originally irradiated with the electron beams. As a result, the exposed pattern does not match an electron beam irradiation pattern.
As a method for improving the accuracy of drawing a pattern taking the proximity effect mentioned above into consideration, there is a method including the steps of: previously determining density of a pattern to be drawn; smoothing the determined density, thereby calculating the amount of overexposure due to the proximity effect; and suppressing the dose of electron beams to be applied to a portion to be overexposed, based on the calculated amount of overexposure, as disclosed in, for example, Japanese Patent Application Publication Nos. Hei 8 (1996)-213315 and Hei 5 (1993)-308046 and the above publication No. 2000-508839.
On the other hand, an electron beam apparatus, in which a wafer or the like is irradiated with finely focused electron beams so as to observe secondary electrons emitted from the wafer, can inspect a graphic pattern drawn on the wafer by utilizing the fact that the amount of secondary electrons varies depending on the inclination of the surface of the wafer. Such electron beam apparatuses include an apparatus disclosed in Japanese Patent Application Publication No. Hei 9 (1997)-166428, showing a method for performing high-precision measurement by extrapolating the effect of electrostatic charge or the like due to electron beam irradiation and variations in measured dimensions.
Moreover, Japanese Patent Application Publication Nos. 2003-257355 and 2003-346698, for example, disclose a multiple-beam type electron beam apparatus which simultaneously irradiates a sample such as a wafer with a plurality of electron beams, thus performing high-speed observation on the sample.    [Patent Literature 1] Japanese Patent Application Publication No. Hei 11 (1999)-40485    [Patent Literature 2] Japanese Patent Application Publication No. Hei 11 (1999)-195589    [Patent Literature 3] Japanese Patent Application Publication No. 2000-508839    [Patent Literature 4] Japanese Patent Application Publication No. Hei 8 (1996)-213315    [Patent Literature 5] Japanese Patent Application Publication No. Hei 5 (1993)-308046    [Patent Literature 6] Japanese Patent Application Publication No. Hei 9 (1997)-166428    [Patent Literature 7] Japanese Patent Application Publication No. 2003-257355    [Patent Literature 8] Japanese Patent Application Publication No. 2003-346698